lots of good advice here already,.
Couple of things I would add if they are not said already.

When decelerating with the throttle closed like coming up to junctions roundabouts etc don't use the gearbox to slow down.
Pull the clutch in and use the brakes and give the engine a few blips of the throttle to increase fuel to the engine .

On deceleration with the throttle closed the engine can still be turning over at 3000-4000 rpm but there is only the tiny Pilot jet providing any cooling lubricating fuel and often its not enough especially in hot weather.

Second thing try and see if you can get your flywheel cowl closer to the fan blades. The closer the cowl the more air is drawn over the engine . Some recommend as little as 2mm !

Something else you can try is change your spark plug for a cooler one in the range and also screw your air mix screw in a turn to richen the idle mixture .

blast !... sorry I didn't see that 4th page and my previous response . Wish to god the damn editing period was a few seconds longer its so annoying not to be able to edit ones post a few seconds after posting if you spot an error or omission or a brainfart like mine lol